The evolution and utilization of estuarine and coastal regions are greatly restricted by sediment problems. This thesis aims to better understand fine sediment transport under combined action of waves and currents, especially in the wave-current bottom boundary layer (BBL). Field observations, experimental data analysis, theoretical analysis and numerical models are employed. Silt-dominated sediments are sensitive to flow dynamics and the suspended sediment concentration (SSC) increase rapidly under strong flow dynamics. This research unveils several fundamental aspects of silty sediment, i.e., the criterion of the incipient motion, the SSC profiles and their phase-averaged parameterization in wave-dominated conditions. An expression for sediment incipient motion is proposed for silt-sand sediment under combined wave and current conditions. A process based intra-wave 1DV model for flow-sediment dynamics near the bed is developed in combined wave-current conditions. The high concentration layer (HCL) was simulated and sensitivity analysis was carried out by the 1DV model on factors that impact the SSC in the HCL. Finally, based on the 1DV model, the formulations of the mean SSC profile of silt-sand sediments in wave conditions were proposed. The developed approaches are expected to be applied in engineering practice and further simulation.
1.2. Behaviour of sediments with different grain sizes
1.3. Wave-current bottom boundary layer (BBL)
1.4. Numerical simulation for sediment transport under combined waves and currents
1.5. Key problems in sediment transport modelling
1.6. Objectives and research questions
1.7. Thesis organization
2 Sediment transport in silt-dominated coastal areas: field works and data analysis
2.2. Field works and data analysis in northwestern Caofeidian sea area of Bohai bay
2.3. Collected field data in some silt-dominated coasts
3 Incipient motion of silt-sand under combined action of waves and currents
3.2. Analysis of sediment incipient motion under waves and currents
3.4. Verification and discussion
3.5. Conclusion and remarks
4 High sediment concentration layer of fine sediments: modelling by a 1DV model
4.2. A 1DV model for flow-sediment movement in wave-current BBL
4.3. Model verification
4.4. Sensitivity analysis and discussion: factors that impact the sediment concentration profile of the HCL
5 The mean SSC of silty sediments under wave-dominated conditions
5.2. Methods and Materials
5.3. Mean sediment concentration profile under different bed forms
5.4. Depth-averaged sediment concentration under waves
6 Conclusions and recommendations
Appendix A. Derivation of Reynolds equation for wave-current motions
Appendix B. Time varying functions of the eddy viscosity and the reference concentration
Appendix C. The formula for reference concentration
Appendix D. Description of the 1DV model
Appendix E. The procedures of depth-averaged SSC in Matlab script
IHE Delft PhD programme leads to a deepening of a field of specialisation. PhD fellows do scientific research, often with conclusions that directly influence their region. At IHE Delft, PhD researchers from around the world participate in problem-focused and solution-oriented research on development issues, resulting in an inspiring research environment. PhD fellows work together with other researchers from many countries dealing with topics related to water and the environment.
PhD research is often carried out in the ‘sandwich’ model. Preparation and final reporting – the first and last portion of the programme – are carried out in Delft, while actual research is done in the fellow’s home country, under co-supervision of a local institute. Regular contacts with the promotor are maintained through visits and long-distance communication. This enables researchers to employ solutions directly to problems in their geographical region.
IHE Delft PhD degrees are awarded jointly with a university. The degrees are highly valued and fully recognised in all parts of the world.